Here are some alternate pool games I have developed (with help from Ryu):

"Best-of-7"
This is superficially similar to 9-ball, in that the lowest ball on the table must be the first struck with the cue-ball. However, it is played with 7 (seven) balls, and the goal here is to be the first to sink 4 (four) balls -- i.e. win the "best of seven" game. The balls are arranged in "V" with the 1-ball at the point, and the 7 at one of the ends. Scratches are "ball-in-hand," any ball sunk "illegally" (i.e. on a scratched shot, or on shots where the lowest ball remaining on the table wasn't struck first) are placed back on the table at the dot.
The first break is determined by coin-flip or paper-rock-scissors or some such thing. Subsequent breaks are made by the loser of the last game. The Match is, of course, best of seven games. (although, frankly, there is no reason that can't be modified to best of three, five, nine, or whatever -- thus rendering the game, for example, Best of 7/Best of 5).

"Best-of-5"
Virtually the same game as "Best-of-7" except, of course, 5 balls are used, and the winner of the game is the first person to sink 3 balls. Match is best of five games. Balls are again arranged in a "v" with the 1-ball at the point and the 5-ball at one of the points.

"3-ball"
This is a rapid-fire game. Three balls arranged in a triangle, they must be sunk in numerical order, and the person to sink 2 of the three scores one point. If somone sinks all three, they score 2 (two) points. First person to 7 wins (although really any number over two will work, whatever you decide). Opening break is decided as above, with subsequent breaks by the person who lost the last round.
Please note the distinction, however, that the balls must be sunk in numerical order and not just "lowest ball struck first" as in nine-ball, et all. A ball not sunk in numerical order will be treated as a "scratch" and the ball will be placed at the dot, with ball-in-hand for the opponent.

"Goals"
At its simplest, this game is modified slop. The objective is to score 21 points, by sinking balls in your end of the table. Balls sunk in your opponent's end, even by you, score for them. Balls sunk in the middle pockets count for nothing; BUT sinking balls in any pocket (even your opponent's) allows you to keep the shot, and balls hit into the side pockets reduce the number of potential points on the table (advantageuous if you have the lead). Balls sunk on scratched shots count as points, but obviously you don't get to keep the shot, and a scratch is "ball in hand" for your opponent.
Opening break is determined by the usual coin-flip/paper-rock-scissors method, with subsequent breaks made by the person in the lead (if tied, it alternates from whoever broke last). The person NOT breaking gets to pick his end, of course, so I suppose to winner of the opening coin-flip would want to pick his end instead, which is perfectly acceptable.

there are, obviously, numerous permutations of the above games. For instance, one can make a simple modification to "Best-of-7" stipulating the balls must be sunk in numerical order, or one can remove the nine-ball-esque "balls struck in order" from Best-of-7 or Best-of-5, as well as play "Best-of-9" or whatever. One could change to target score in "Goals" to anything, really, and even reduce the number of balls on the table.
I kind of like a "tournament" format for "Best-of-7" or "-5" wherein three or four people can be involved, and no-one has to stand around waiting for very long. With three people, you could just play 1 game at a time, with the winner keeping the table. With four people, you could play "mini-tournaments" with person 1 vs 2, and person 3 vs. 4, then the winners of those two games playing... repeat ad-naseum.